A switch-mode power converter (also referred to as a “power converter”) is a power supply or power processing circuit that converts an input voltage waveform, such as an ac input voltage waveform, into a specified output voltage waveform, such as a dc output voltage waveform. Controllers associated with the power converters manage an operation thereof by controlling the conduction periods of power switches employed therein. Generally, the controllers are coupled between an input and output of the power converter in a feedback loop configuration.
Typically, the controller measures an internal operating characteristic (e.g., an internal bus voltage) or an output characteristic, (e.g., an output voltage or an output current) representing an operating condition of the power converter, and based thereon modifies a duty cycle of a power switch or power switches of the power converter to regulate an internal operating characteristic or the output characteristic. The duty cycle is a ratio represented by a conduction period of a power switch to a switching period thereof. Thus, if a power switch conducts for half of the switching period, the duty cycle for the power switch would be 0.5 (or 50 percent). Additionally, as the needs for systems such as a microprocessor powered by the power converter dynamically change (e.g., as a computational load on the microprocessor changes), the controller should be configured to dynamically increase or decrease the duty cycle of the power switches therein to regulate the internal or the output characteristic at a desired value. In an exemplary application, the power converters have the capability to convert an unregulated ac input voltage, such as a nominal 240 volts ac, to a regulated, dc output voltage such as 400 volts, to power a load, which may include a further stage of power conversion, such as a dc-to-dc converter.
A new consideration for the design of a power converter in certain applications is the need for the power converter to estimate accurately an input power thereto averaged over a period of the input waveform, with an accuracy of, for instance, a few percent. The power converter may communicate the input power estimate to a system external to the power converter. Hence, there is a need to incorporate such input power estimation capability into a power converter.
The need to estimate accurately an input power to a power converter is a parallel need to the general objective to reduce energy consumed by an electronic system Power converter designers in the past have inadequately responded to this new design requirement. A particular technique that has been used to estimate input power averaged over an input voltage waveform includes sensing instantaneous input current and voltage to the power converter and forming an integral over a cycle of the input voltage waveform of a product of the instantaneous input current and voltage. This approach can entail a substantial amount of added signal processing, particularly when implemented with digital circuit elements.
The allocation of a digital resource in a high-performance, cost competitive application may be made on a priority basis in view of the basic control needs of the power converter, and may reluctantly be used as an auxiliary computation-intensive task such as estimation of power converter input power by integrating a product of waveforms. Producing an accurate estimate of input power to a power converter, particularly in a digital control application, without consuming valuable additional computing resources can have immediate effects on the applicability and marketplace acceptance of a particular power converter design.
A controller for a power processing circuit is presently not available that estimates input power without substantial signal processing overhead. Accordingly, what is needed in the art is a controller for a power processing circuit that can provide an estimate of the input power without consuming substantial signal processing resources.